Building board and method for producing the same

ABSTRACT

A building board includes a base material, an insulating coating film for covering a surface of the base material, and a transparent clear coating film for covering the insulating coating film. The insulating coating film contains a coating film forming material, organic hollow particles, and a water-soluble solvent. The method for producing the building board includes a step of forming an insulating coating film in which an insulating paint is applied to a surface of the base material and then dried to form the insulating coating film, and a step of forming a clear coating film in which a clear paint is applied to a surface of the insulating coating film and then dried to form the clear coating film. The insulating paint contains a coating film forming material, organic hollow particles, and a water-soluble solvent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a building board that is used forexterior walls and the like of buildings, and a method for producing thebuilding board.

2. Description of the Related Art

In recent years, there is a demand for improvement of thermal insulationeffect for building boards used for exterior walls and roofs ofbuildings such as residential houses in view of environmental problemssuch as energy conservation. To this end, it has been considered that aninsulating coating film is formed on the surface of the building board.

For example, JP 2000-71389A proposed an insulating wall materialobtained by forming, on the surface of a base material, an insulatingcoating film containing mixed and dispersed fine ceramic particleshaving a thermal insulation effect in a coating film forming material.

SUMMARY OF THE INVENTION

However, it was found from the results of experiments conducted by theinventors that the actual thermal insulation effect of the buildingboard on which the insulating coating film containing mixed anddispersed fine ceramic particles was formed as described above was small(see the experiment described below). As a result of intensive researchconducted by the inventors, it was found that one of the reasons was thefact that a hollow ratio of fine ceramic particles tends to become low,and therefore a thermal insulation effect is hard to be obtained.

Furthermore, superior weatherability is required so that building boardsare used for exterior walls, roofs, or the like of buildings.

The present invention was made in view of these backgrounds, and it isan object thereof to provide a building board that has superior thermalinsulation properties and weatherability, and a method for producing thebuilding board.

An aspect of the present invention is a building board including a basematerial, an insulating coating film for covering a surface of the basematerial, and a transparent clear coating film for covering theinsulating coating film, wherein the insulating coating film contains acoating film forming material, organic hollow particles, and awater-soluble solvent.

Another aspect of the present invention is a method for producing abuilding board including a base material, an insulating coating film forcovering a surface of the base material, and a clear coating film forcovering the insulating coating film, and the method includes a step offorming an insulating coating film in which an insulating paint isapplied to a surface of the base material and then dried to form theinsulating coating film, and a step of forming a clear coating film inwhich a clear paint is applied to a surface of the insulating coatingfilm and then dried to form the clear coating film, wherein a paintcontaining a coating film forming material, organic hollow particles,and a water-soluble solvent whose boiling point is higher than atemperature of the coating film when the coating film is dried in thestep of forming an insulating coating film and the step of forming aclear coating film is used as the insulating paint.

In the building board described above, the insulating coating filmincludes organic hollow particles. Thereby, the thermal insulationfunction is provided to the insulating coating film. Since the organichollow particles include an organic material, the hollow ratio thereoftends to become high. That is, since organic materials are flexible, thematerials easily stretch when hollow particles are formed, so that thehollow ratio thereof is able to be high. Therefore, the thermalinsulation effect of organic hollow particles is large, and the thermalinsulation properties of the insulating coating film can be improved.

Since the insulating coating film contains a water-soluble solvent, thehomogeneous insulating coating film can be formed. That is, mixing oforganic hollow particles having the high thermal insulation effecttherein as described above may be considered to cause a problem in thatit is hard to uniformly transmit heat to the entire coating wheninsulating paint is dried after being applied to a base material.Accordingly, the water-soluble solvent is contained in the insulatingcoating film, so that heat is easily transmitted to the entire coatingwhen the paint is dried. Therefore, a homogeneous insulating coatingfilm can be formed. Thereby, a homogeneous thermal insulation effect canbe obtained by the insulating coating film all over the building board,and therefore the thermal insulation properties of the building boardcan be improved as a whole.

The building board includes a transparent clear coating film forcovering the insulating coating film. Thereby, the weatherability of thebuilding board can be improved. Moreover, since the clear coating filmis transparent, the clear coating film neither stores heat nor inhibitsthe thermal insulation effect of the insulating coating film. That is,the weatherability of the building board can be improved without thethermal insulation effect being inhibited by forming the clear coatingfilm.

In the method for producing the building board, the insulating paintused in the step of forming the insulating coating film contains acoating film forming material, organic hollow particles and awater-soluble solvent. Thereby, as described above, the thermalinsulation effect of the insulating coating film can be improved toproduce the building board having the superior thermal insulationproperties.

Note that the boiling point of the water-soluble solvent is higher thanthe temperature of the coating film when the coating film is dried inthe step of forming the insulating coating film and the step of formingthe clear coating film. Therefore, even after the coating film is driedin each step, the water-soluble solvent remains sufficiently, and cancontribute to the formation of the homogeneous insulating coating film.

As described above, with the present invention, a building board havingsuperior thermal insulation properties and weatherability, and a methodfor producing the building board can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a building board ofExample 1.

FIG. 2 is a schematic cross-sectional view of a building board ofExample 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the method for producing the building board described above, thetemperature of the coating film refers to the temperatures of theinsulating coating film and the clear coating film.

The water-soluble solvent includes at least one of a glycol-basedsolvent and a glycol ether-based solvent, and can effectively achievethe formation of the homogeneous insulating coating film. That is, theglycol-based solvent and glycol ether-based solvent have a high boilingpoint and tend to remain until the end of the step of forming theinsulating coating film. Therefore, the glycol-based solvent and glycolether-based solvent may contribute to homogenization of the insulatingcoating film.

It is preferable that the organic hollow particles include at least oneof acrylonitrile, methacrylonitrile, vinylidene chloride, acrylic ester,and styrene. In this case, it is possible to especially stably obtainthe organic hollow particles in which the hollow ratio is high.

The average hollow ratio of the organic hollow particles is 80% or more,and the insulating coating film can provide a sufficient thermalinsulation effect.

It is preferable that the average hollow ratio is 90% or more. In thiscase, the insulating coating film can provide an even better thermalinsulation effect. Furthermore, a preferable upper limit of the averagehollow ratio varies due to various factors as long as the hollow stateof the organic hollow particles can be maintained.

Note that the average hollow ratio is a value expressed as a percentageby volume. The same applies hereinafter.

A transparent hydrophilic coating film may be formed as an outermostlayer so as to cover the clear coating film. In this case, an appearancedesign of the building board can be maintained for a long time. That is,the hydrophilic coating film described above is formed as the outermostlayer, so that, even if dirt is attached to the surface of the buildingboard, namely, the surface of the hydrophilic coating film, water isabsorbed into the hydrophilic coating film, and the dirt runs downtogether with water, by water being poured on the surface of thebuilding board or by rainwater falling thereon. Therefore, theappearance of the building board can be maintained for a long time.Furthermore, dirt attached to the surface of the building board caneasily run down together with water to suppress a thermal storage effecton the surface of the building board.

Since the hydrophilic coating film is transparent, the thermalinsulation properties of the building board can be secured without thefunction of the insulating coating film being impaired.

In the method for producing the building board, it is preferable thatthe temperature of the coating film is not more than 130° C. when thecoating film is dried in the step of forming the insulating coating filmand the step of forming the clear coating film. In this case, whilereliably securing the hollow state of the organic hollow particles, itis possible to form the insulating coating film. Therefore, the thermalinsulation properties of the building board can be reliably obtained.Furthermore, when the coating film is dried, volatilization of thewater-soluble solvent contained in the insulating paint is easilysuppressed. Therefore, the insulating coating film can be reliablyhomogenized.

It is preferable that the temperature of the coating film is set to 40to 110° C. when the coating film is dried in the step of forming theinsulating coating film and the step of forming the clear coating filmin consideration of the heat resistant temperature of the organic hollowparticles.

The method for producing the building board may further include a stepof forming a hydrophilic coating film in which a hydrophilic paint isapplied to the surface of the clear coating film and then dried to formthe transparent hydrophilic coating film as the outermost layer. In thiscase, the appearance design of the building board can be maintained fora long time.

EXAMPLES Example 1

An example of the building board and the method for producing thebuilding board described above will be described with reference to FIG.1.

A building board 1 of the present example includes a base material 2, aninsulating coating film 3 for covering a surface of the base material 2,and a transparent clear coating film 4 for covering the insulatingcoating film 3.

The insulating coating film 3 contains a coating film forming material,organic hollow particles, and a water-soluble solvent.

The building board 1 can be used for, for example, exterior walls orroofs of buildings.

Examples of the base material 2 include a ceramic siding board such as awood fiber-reinforced cement board, a fiber-reinforced cement board, afiber-reinforced cement calcium silicate board, and a slag gypsum board;a metallic siding board; and an ALC board.

A sealer layer 21 is formed on the surface of the base material 2. Thesealer layer 21 can be constituted by, for example, an acrylic resinemulsion paint, an acrylic urethane resin-based paint, an epoxyresin-based paint, a solvent-type moisture-curable urethane, and a waterdispersion-type isocyanate. Note that the sealer layer 21 may beconstituted by one layer, but can include two or more layers.

The insulating coating film 3 having an average film thickness of 5 to500 μm is formed on the sealer layer 21 of the base material 2. It ismore preferable that the average film thickness of the insulatingcoating film 3 is 50 to 500 μm. Thereby, it is possible to obtain thesufficient thermal insulation effect and, prevent the insulating coatingfilm 3 from being easily cracked due to a long drying time.

Examples of the coating film forming material s that mainly constitutethe insulating coating film 3 include a synthetic resin such as anacrylic resin, a silicone resin, a fluororesin, an acrylic siliconeresin, a polyurethane resin, and an epoxy resin. The organic hollowparticles are mixed and dispersed in this coating film forming material.

The organic hollow particles include at least one of acrylonitrile,methacrylonitrile, vinylidene chloride, acrylic ester, and styrene. Theaverage hollow ratio of the organic hollow particles is 80% or more. Theaverage hollow ratio of the organic hollow particles is more preferably90% or more.

It is preferable that the content of the organic hollow particles is0.01 to 5.0 parts by mass in consideration of the thermal insulationeffect and coating strength. Here, the content of the organic hollowparticles represents the ratio of organic the solid content forming themembrane of the organic hollow particle with respect to 100 parts bymass of the paint solid content contained in the entire insulatingcoating film. The same applies hereinafter.

It is preferable that the average particle diameter of the organichollow particles is 5 to 50 μm in consideration of the thermalinsulation effect and coating strength.

The water-soluble solvent is contained in the insulating coating film 3.That is, in the building board 1 obtained finally by producing stepsdescribed below, the insulating coating film 3 contains thewater-soluble solvent. The content of this water-soluble solvent is 0.1to 10 parts by mass with respect to 100 parts by mass of the solidcontent of the insulating coating film 3. Thereby, the entire insulatingcoating film 3 can be reliably formed homogeneously.

The water-soluble solvent includes, at least one of a glycol-basedsolvent and a glycol ether-based solvent. That is, examples of thewater-soluble solvent include ethylene glycol, propylene glycol,diethylene glycol, dipropylene glycol N-butyl ether, and tripropyleneglycol monomethyl ether, or a mixture thereof.

Furthermore, the insulating coating film 3 contains pigments and servesas a color layer as well. Note that the insulating coating film 3 canalso be a coating film containing no pigments.

The clear coating film 4 is formed of a water-soluble paint. Examples ofthis water-soluble paint include an acrylic silicone resin emulsionpaint, an acrylic resin emulsion paint, a silicone resin-based paint, anacrylic urethane-based paint, a fluororesin-based paint, andpolyurethane resin-based paint.

When the building board 1 of the present example is produced, the stepof forming the insulating coating film and the step of forming the clearcoating film described below are performed.

In the step of forming the insulating coating film, an insulating paintis applied to a surface of the base material 2 (surface of the sealerlayer 21) and then dried to form the insulating coating film 3.

In the step of forming the clear coating film, a clear paint is appliedto a surface of the insulating coating film 3 and then dried to form theclear coating film 4.

The insulating paint is obtained by mixing and dispersing the organichollow particles in the coating film forming material and contains thewater-soluble solvent.

The specific materials of the coating film forming material, the organichollow particles, and the water-soluble solvent that are contained inthe insulating paint, and the clear paint are as described above. Theboiling point of the water-soluble solvent is higher than thetemperature of the coating film when the coating film is dried in thestep of forming the insulating coating film and the step of forming theclear coating film. Conversely, the temperature of the coating film whenthe coating film is dried in the step of forming the insulating coatingfilm and the step of forming the clear coating film is set to less thanthe boiling point of the water-soluble solvent. Specifically, thetemperature of the coating film when the coating film is dried is notmore than 130° C.

Next, the effect of the present example will be described.

In the building board 1 described above, the insulating coating film 3is containing the mixed and dispersed organic hollow particles. Thereby,the thermal insulation function is provided to the insulating coatingfilm 3. Since the organic hollow particles include an organic material,the hollow ratio thereof tends to become high. Therefore, the thermalinsulation properties of the insulating coating film 3 can be improved.

Since the insulating coating film 3 contains a water-soluble solvent,the homogeneous insulating coating film 3 can be formed. That is, thewater-soluble solvent is contained in the insulating coating film 3, sothat heat is easily transmitted to the entire coating when theinsulating paint is dried. Therefore, the homogeneous insulating coatingfilm 3 can be formed. Thereby, the homogeneous thermal insulation effectcan be obtained by the insulating coating film 3 all over the buildingboard 1.

The boiling point of the water-soluble solvent is higher than thetemperature of the coating film when the coating film is dried in thestep of forming the insulating coating film and the step of forming theclear coating film. Therefore, even after the coating film is dried ineach step, the water-soluble solvent remains sufficiently and cancontribute to the formation of the homogeneous insulating coating film.

The water-soluble solvent includes at least one of a glycol-basedsolvent and a glycol ether-based solvent, and can effectively achievethe formation of the homogeneous insulating coating film 3. That is, theglycol-based solvent and glycol ether-based solvent have a high boilingpoint and tend to remain until the end of the step of forming theinsulating coating film. Therefore, the glycol-based solvent and glycolether-based solvent may contribute to homogenization of the insulatingcoating film.

The temperature of the coating film is set to not more than 130° C. whenthe coating film is dried in the step of forming the insulating coatingfilm and the step of forming the clear coating film, and therefore it ispossible to form the insulating coating film while reliably securing thehollow structure of the organic hollow particles. Accordingly, thethermal insulation properties of the building board 1 can be reliablyobtained. Furthermore, when the coating film is dried, volatilization ofthe water-soluble solvent contained in the insulating paint is easilysuppressed. Therefore, the insulating coating film 3 can be reliablyhomogenized.

Since the organic hollow particles include at least one ofacrylonitrile, methacrylonitrile, vinylidene chloride, acrylic ester,and styrene, it is possible to especially stably obtain the organichollow particles in which the hollow ratio is high.

Since the average hollow ratio of the organic hollow particles is 80% ormore, the insulating coating film 3 can be provided with a sufficientthermal insulation effect.

Since the building board 1 includes the transparent clear coating film4, the weatherability of the building board 1 can be improved withoutthe thermal insulation effect by the insulating coating film 3 beinginhibited.

As described above, with the present example, a building board havingsuperior thermal insulation properties and weatherability, and a methodfor producing the building board can be provided.

Example 2

As shown in FIG. 2, the present example is an example in which atransparent hydrophilic coating film 5 is formed as an outermost layerso as to cover the clear coating film 4.

The hydrophilic coating film 5 can be made of, for example, silica,colloidal silica, and fumed silica.

When the building board 1 of the present example is produced, a step offorming the hydrophilic coating film as described below may be added tothe step of forming the insulating coating film and the step of formingthe clear coating film in the producing method of Example 1. That is, inthe step of forming the hydrophilic coating film following the step offorming the clear coating film, a hydrophilic paint is applied to asurface of the clear coating film 4 and then dried to form thetransparent hydrophilic coating film 5 as the outermost layer.

Here, a solution containing, for example, dispersed silica, colloidalsilica, and fumed silica can be used as the hydrophilic paint.

Other respects are the same as those in Example 1.

In the case of the present example, an appearance design of the buildingboard 1 can be maintained for a long time. That is, the hydrophiliccoating film 5 is formed as the outermost layer, so that, even if dirtis attached to the surface of the building board 1, water is absorbedinto the hydrophilic coating film 5, and the stain runs down togetherwith water, by water being poured on the surface of the building board 1or by rainwater falling thereon. Therefore, the appearance of thebuilding board 1 can be maintained for a long time. Furthermore, dirtattached to the surface of the building board 1 can easily run downtogether with water to suppress a thermal storage effect on the surfaceof the building board 1.

Since the hydrophilic coating film 5 is transparent, the thermalinsulation properties of the building board 1 can be secured without thefunction of the insulating coating film 3 being impaired.

Other effects that are the same as those in Example 1 are included.

EXPERIMENTS

The present example is an example in which the thermal insulationproperties of the building boards shown in Example 1 and Example 2described above are evaluated.

As shown in Table 1, the building boards of Example 1 or Example 2 areproduced as Samples 1 to 5 by variously changing the insulating coatingfilm (insulating paint), the clear coating film (clear paint), and thehydrophilic coating film (hydrophilic paint).

Furthermore, as shown in Table 2, the building boards of Example 1 inwhich an insulating coating film (insulating paint) has a constitutiondifferent from that of the insulating coating film shown in Example 1are produced as Samples 6 to 10.

Note that, in all the samples, the base material is a wood fiberreinforced cement board, and the surface thereof is coated with anacrylic resin emulsion paint (white) to form the sealer layer. Theinsulating coating film is formed on the sealer layer. Sample 5 containsno pigments, and all the others contain white pigments. That is, theinsulating coating film of Sample 5 is transparent, and the insulatingcoating film is a white color layer in all the other samples.

Details of the samples are as described in Table 1 and Table 2. InSamples 1 to 9, the coating film forming materials in the insulatingcoating film (insulating paint) and in the clear coating film (clearpaint) include acrylic silicone emulsion. Sample 10 is provided with noclear coating film. The hydrophilic coating film of Sample 5 includessilica, and a solution containing dispersed colloidal silica is used asthe hydrophilic paint for forming the hydrophilic coating film. Thehollow particles of Sample 2 include vinylidene chloride andacrylonitrile. The hollow particles of Sample 3 includemethacrylonitrile and methyl acrylate.

The hollow particles that is mixed and dispersed in the insulatingcoating film (insulating paint) of Sample 6 are ceramics. Solidparticles are mixed and dispersed in the insulating coating film(insulating paint) of Sample 8 instead of the hollow particles.

Furthermore, in Table 1 and Table 2, the content of the hollow particles(solid particles) and the content of the water-soluble solvent arerepresented by parts by mass with respect to 100 parts by mass of thepaint solid content.

Problems such as production of cracks, deterioration of the thermalinsulation performance, and an appearance inferiority occurred in theinsulating coating film of Sample 9 in which the insulating paintcontained no water-soluble solvent.

The thermal insulation effect test was performed on the building boardsof Samples 1 to 10.

A lamp irradiating method was used as the testing method. That is, thesample surface was irradiated with light by a halogen lamp of 100 V and150 W disposed at a position 10 cm away from the sample surface. Whenthe sample surface was continuously irradiated with light for 10minutes, a temperature of the sample surface was measured using aradiation thermometer. The results are shown in Table 1 and Table 2.

TABLE 1 Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Insulating HollowComposition Acrylonitrile Vinylidene Methacrylonitrile AcrylonitrileAcrylonitrile paint particles chloride and and acrylonitrile methylacrylate Average 20 20 40 15 15 particle diameter (μm) Average hollow 9898 98 98 98 ratio (%) Content 2.0 5.0 0.5 2.0 2.0 (parts by mass)Water-soluble Solvent type Ethylene glycol Propylene glycol Diethyleneglycol Dipropylene Tripropylene solvent glycol N-butyl glycol ethermonomethyl ether Content 2.0 0.2 10.0 2.0 2.0 (parts by mass) Coatingfilm Composition Acrylic silicone Acrylic silicone Acrylic siliconeAcrylic silicone Acrylic silicone forming emulsion emulsion emulsionemulsion emulsion material Insulating Film thickness (μm) 50 30 500 5050 coating film Clear coating film Acrylic silicone Acrylic siliconeAcrylic silicone Acrylic silicone Acrylic silicone emulsion emulsionemulsion emulsion emulsion Hydrophilic coating film Absent Absent AbsentAbsent Present Physical Surface temperature (° C.) 55 56 50 54 54properties Gloss retention ratio Good Good Good Good Good

TABLE 2 Sample 6 Sample 7 Sample 8 Sample 9 Sample 10 Insulating HollowComposition — Ceramic Methyl acrylate Acrylonitrile Acrylonitrile paintparticles (solid) Average — 150 20 20 20 particle diameter (μm) Averagehollow — 30 0 98 98 ratio (%) Content — 5.0 2.0 2.0 2.0 (parts by mass)Water-soluble Solvent type — Propylene glycol Ethylene glycol — Ethyleneglycol solvent Content — 2.0 2.0 — 2.0 (parts by mass) Coating filmComposition Acrylic silicone Acrylic silicone Acrylic silicone Acrylicsilicone Acrylic silicone forming emulsion emulsion emulsion emulsionemulsion material Insulating Film thickness (μm) 20 50 100 100 50coating film Clear coating film Acrylic silicone Acrylic siliconeAcrylic silicone Acrylic silicone Absent emulsion emulsion emulsionemulsion Hydrophilic coating film Absent Absent Absent Absent AbsenttPhysical Surface temperature (° C.) 65 63 63 60 55 properties Glossretention ratio Good Good Good Good Poor

As shown in Table 1 and Table 2, the surface temperatures of Samples 6to 9 reached 60 to 65° C., whereas the surface temperatures of Samples 1to 5 fell within the range of 50 to 56° C. That is, the constitutions ofExample 1 and Example 2 can be used to reliably suppress rise intemperature of the building board, and it can be said that the thermalinsulation properties thereof can be improved thereby.

Weatherability of the building board was evaluated. Weatherabilitythereof was evaluated using the degree of changes of the gloss value(gloss retention ratio), as an evaluation method, on the surface of thebuilding board before and after a predetermined durability test wasperformed.

Specifically, the test below was performed using Samples 1 to 10described above.

First, gloss values at random five points on the surface of the buildingboard (coating surface) were measured using a hand-held gloss checker“Gloss Checker IG-320” manufactured by HORIBA, Ltd. The average of thesevalues was taken as an “initial average gloss value”.

Next, an accelerated test (cycle of irradiation for 4 hours and wettingfor 4 hours) was performed on each sample for 800 hours using “MetalWeather Meter” manufactured by Daipla Wintes Co., Ltd. Here, theirradiation condition is set to an irradiation intensity of 1,100 W/m²,an irradiation distance of 240 mm, and a black panel temperature of 63°C. The wetting condition is set to a condensation temperature of 30° C.and a condensation humidity of 98%, and the samples were showered for 10seconds before and after condensation.

After the accelerated test described above, gloss values at random fivepoints on the sample surface (coating surface) were measured using theabove hand-held gloss checker similarly to before the accelerated test,and the average of these values was taken as an “average gloss valueafter weatherability test”.

A gloss retention ratio was calculated using the calculation formulabelow.

Gloss retention ratio(%)=(average gloss value after weatherabilitytest)/(initial average gloss value)

The gloss retention ratio calculated was evaluated as described below,and the results of evaluation were described in Table 1 and Table 2.

Good: the gloss retention ratio is 80% or more.

Fair: the gloss retention ratio is 50% or more but less than 80%.

Poor: the gloss retention ratio is less than 50%.

As shown in Table 1 and Table 2, the gloss retention ratio of Sample 10including no clear coating film was less than 50%, whereas all of thegloss retention ratios of Samples 1 to 9 including the clear coatingfilm were 80% or more. That is, Samples 1 to 9 including the clearcoating film retain the initial gloss even after the weatherability test(accelerated test) is performed thereon, and it can be said that Samples1 to 9 have superior weatherability.

These results show that weatherability can be improved by forming theclear coating film.

What is claimed is:
 1. A building board comprising: a base material; aninsulating coating film for covering a surface of the base material; anda transparent clear coating film for covering the insulating coatingfilm, wherein the insulating coating film contains a coating filmforming material, organic hollow particles, and a water-soluble solvent,the organic hollow particles have an average hollow ratio of 80% or moreand an average particle diameter of 5 to 50 μm, and the water-solublesolvent is at least one of a glycol-based solvent and a glycolether-based solvent.
 2. The building board according to claim 1, whereinthe organic hollow particles comprise at least one of acrylonitrile,methacrylonitrile, vinylidene chloride, acrylic ester, and styrene. 3.The building board according to claim 1, wherein the insulating coatingfilm contains 0.01 to 5.0 parts by mass of the organic hollow particleswith respect to 100 parts by mass of solid content thereof.
 4. Thebuilding board according to claim 1, wherein the insulating coating filmhas an average film thickness of 5 to 500 μm.
 5. The building boardaccording to claim 1, wherein a transparent hydrophilic coating film isformed as an outermost layer so as to cover the clear coating film. 6.The building board according to claim 5, wherein the hydrophilic coatingfilm is constituted by at least one of silica, colloidal silica, andfumed silica.
 7. The building board according to claim 1, wherein thebase material is a ceramic siding board.
 8. A method for producing abuilding board comprising a base material, an insulating coating filmfor covering a surface of the base material, and a clear coating filmfor covering the insulating coating film, the method comprising: a stepof forming an insulating coating film in which an insulating paint isapplied to a surface of the base material and then dried to form theinsulating coating film; and a step of forming a clear coating film inwhich a clear paint is applied to a surface of the insulating coatingfilm and then dried to form the clear coating film, wherein a paintcontaining a coating film forming material, organic hollow particles,and a water-soluble solvent whose boiling point is higher than atemperature of the coating film when the coating film is dried in thestep of forming an insulating coating film and the step of forming aclear coating film is used as the insulating paint, the organic hollowparticles have an average hollow ratio of 80% or more, and an averageparticle diameter of 5 to 50 μm, and the water-soluble solvent is atleast one of a glycol-based solvent and a glycol ether-based solvent. 9.The method for producing a building board according to claim 8, whereinthe temperature of the coating film is set to not more than 130° C.°when the coating film is dried in the step of forming an insulatingcoating film and the step of forming a clear coating film.
 10. Themethod for producing a building board according to claim 8, wherein theorganic hollow particles comprise at least one of acrylonitrile,methacrylonitrile, vinylidene chloride, acrylic ester, and styrene. 11.The method for producing a building board according to claim 8, whereinthe insulating paint contains 0.01 to 5.0 parts by mass of the organichollow particles with respect to 100 parts by mass of solid contentthereof.
 12. The method for producing a building board according toclaim 8, further comprising a step of forming a hydrophilic coating filmin which a hydrophilic paint is applied to a surface of the clearcoating film and then dried to form a transparent hydrophilic coatingfilm as an outermost layer.
 13. The method for producing a buildingboard according to claim 12, wherein the hydrophilic paint is a solutionin which at least one of silica, colloidal silica, and fumed silica isdispersed.
 14. The method for producing a building board according toclaim 8, wherein the base material is a ceramic siding.